1. Field of the Invention
This invention relates to loose-leaf binders for pages of partially overlapping strip sheet material in particular binders such as are used to hold accounting ledgers.
2. Description of the Prior Art
Visible record binders such as the type commonly used to record accounting information have narrow sheets which partially overlap each other leaving a visible border along the edges of all of the sheets on which the information to be recorded is written. The overlapping sheets thus present a list of names, titles or other information which is visible at a glance without the necessity of turning through a large sheaf of pages or cards to obtain the desired information. Ordinary binders having sheets therein of identical size only present information on one page at a time, and are therefore impractical for use when information on a number of pages is desired to be viewed at once.
The overlapping pages are held in such binders by a plurality of prongs mounted on upper and lower covers of the binder and extending through perforations in the pages. The prongs are generally maintained in a closed loop to prevent accidental removal of pages by a relatively heavy and usually expensive locking means, which is generally operated from the top and bottom of the binder. Use of such a locking and release mechanism required that the cover structures holding the prongs be sturdy, resulting in covers for such binders comprised of generally thick material. When the binder is full of pages, operation of such locking devices is somewhat clumsy, and because such devices contain a number of parts in sliding relationship, they are rather fragile and easily dislocated.
Another disadvantage of binders known in the art is that because of the overlapping nature of the sheets contained therein, the sheaf of pages in the binder is not of uniform thickness. Generally, the sheaf will be thickest at a central portion where the number of overlapping pages is greatest, and decreases in thickness toward the top and bottom of the sheaf, where the number of overlapping pages decreases. This presents two problems. The first is that the binder covers rest only against the thickest portion of the sheaf, so that handling and storage of such binders puts uneven pressure on the binder cover frequently resulting in stresses which shorten the usable life of the binder. A second problem resulting from the uneven thickness of the pages is that an uneven writing surface is presented for recording information on the borders of the overlapping pages. This not only results in uncomfortable writing for the information recorder, but also may impair the legibility of the information recorded.